A turbo generator is known from EP 1 742 330 A1, for example. It has a drivable, rotatably mounted rotor, also referred to as a runner, and a fixed stator surrounding the rotor, also referred to as a stationary component. The rotor comprises a cylindrical rotor shaft that thickens in the center in the longitudinal direction of the shaft to form a rotor body. The rotor body is also referred to as a runner body. An excitation winding, which can be supplied with a current, is arranged on the rotor body. The stator has a stator winding. To generate electrical energy, the rotor shaft is coupled to a drive, in particular to a drive shaft of a turbine. In this way, it is possible to impart a rotary motion to the rotor relative to the fixed stator. When a current flows through the rotor, a magnetic rotary field is produced, inducing an electric current in the stator winding. Nowadays, a turbo generator has an electric power of between 100 MW and 1500 MW.
U.S. Pat. No. 3,119,033 has disclosed the practice of providing the cylindrical surface of the rotor body with grooves extending in the longitudinal direction of the shaft and spaced apart in the circumferential direction and of arranging the excitation coil in these grooves. For this purpose, a plurality of conductor bars extending in the longitudinal direction of the shaft and insulated from each other are stacked one above the other in the grooves. Toward the cylindrical surface of the rotor body, a groove-sealing key inserted into a profile is provided to secure the conductor bars against the centrifugal forces that prevail during the rotation of the rotor.
DE-B 1 036 997 has disclosed the practice of connecting the ends of conductor bars mounted in adjacent grooves to one another by way of tangential conductors extending in the circumferential direction of the shaft in order to form the excitation winding. The conductor bars are connected to the tangential conductors by soldering, in particular. The tangential conductors are mounted on a shaft neck formed between the shaft end and the shoulder of the rotor body. They form what is known as an end winding. They are secured by a rotor cap against the centrifugal forces prevailing during the rotary motion of the rotor.
As current flows through the excitation winding, a large amount of heat is produced, and this must be removed to ensure trouble-free operation and to exploit the full power potential of the turbo generator. For this purpose, the excitation winding is cooled. Thus, U.S. Pat. No. 3,119,033, which has already been cited, discloses providing some free space for a feeding duct between the bottom of each groove and the end of the excitation winding facing away from the cylindrical surface. Cooling ducts which penetrate the excitation winding and connect the feeding duct to respective outlets in the cylindrical surface of the rotor body are provided substantially in the radial direction of the rotor body. For this purpose, the conductor bars of the excitation winding are provided with apertures, bores or slots that come to lie at least partially one above the other when the conductor bars are arranged in the groove, thereby forming the continuous cooling ducts. The excitation winding is then cooled by feeding a cooling gas, generally air or hydrogen, to the feeding duct. As seen from the feeding duct, the cooling gas then flows through the cooling ducts toward the outlets thereof and, in the process, removes the waste heat produced by the excitation winding. The cooling gas heated by the waste heat flows via the outlets into the space between the rotor and the stator, which fauns a gas collecting space for the cooling gas.
DE 197 32 949 A1 has disclosed the practice of surrounding the stator and the rotor with a common gastight housing. Respective fan impellers are mounted on the two shaft ends. This shaft impeller corotates in the manner of an axial fan as the rotor rotates. In this way, the cooling gas is as it were drawn from entry points in the region of the feeding ducts, via the cooling ducts and the space between the rotor and the stator, which acts as a gas collecting space. The cooling system of the rotor is thus designed as a suction cooling system.
The larger the design of rotor, the longer are the flow paths that have to be traveled by the cooling gas in the feeding ducts and in the excitation winding. In a corresponding manner, a large rotor necessitates a suction fan with a higher power in order to deliver an appropriate quantity of cooling gas through the feeding ducts and then through the cooling ducts. However, it is not possible to arbitrarily increase the power of the fan impellers seated on the rotor shaft since it is coupled to the speed of rotation of the rotor shaft.